The present invention relates to a well drilling tool for use on hollow continuous non-rotating drill strings and in particular to a percussion tool powered by pressurized fluids supplied through the hollow drill string in combination with a generic, fluid powered rotary drilling motor.
Downhole rotary fluid powered drilling motors of several types are in use today and others are being developed for application on non-rotating drill strings in oil well servicing and open hole earth borings. Also, there are a number of different types of surface rotated percussion drills in use today mostly in water-well drilling, blast hole drilling and the like, which have proven to be effective, especially where weight forces on the bit are limited. When downhole motors alone are used on continuous coil tubing strings, weight forces on the drill bit are limited. Also in highly deviated or horizontal wells, bit weight is limited and drill bit penetration rates are consequently reduced.
Downhole percussion tools are presently used on surface rotated drill strings, where the extended length of tubing xe2x80x9cwinds-upxe2x80x9d as a spring, under torsional loading. This quick reacting xe2x80x9cwound-upxe2x80x9d torque discourages axial slip in a splined connection, while at the same time, the elasticity and inertia of the long drill stem soften the sharp hammer blows and would otherwise break loose the static spline friction. Thus, a surface rotary drive is never adequately isolated from the axial hammering of a downhole percussion tool.
Presently several types of fluid powered downhole rotary motors are in use and others are being developed for drilling with non-rotating drill strings. Among these are the Moineau progressive cavity type, such as covered by patents U.S. Pat. Nos. 6,241,494 BI and 4,676,725. Experimental and limited usage motors such as the roller rod vane type of patents U.S. Pat. Nos. 5,785,509, 5,833,444, and 5,302,666 BI are other examples of such downhole motors. Yet other examples are the geared vane and geared turbine type of downhole motors described in Martini U.S. Pat. No. 6,520,271. For the purposes of this disclosure, all of these drilling motor types are considered generic as related to the present invention.
Therefore, a first object of the present invention is to provide a percussive tool for use in combination with existing gas powered, rotary drilling motors. A second object of the invention is to provide increased drill penetration rates, particularly with non-rotating drill strings and where bit weight is limited and yet a third object is to achieve effective motor isolation from percussive shock.
The present invention is an automatic fluid powered, reciprocating mass, percussion drilling tool adapted to drive a drill bit forward in sustained repetition when coupled with a generic fluid driven rotary motor so as to enhance the drilling operation in accordance to the afore stated objects. The industry is moving to increased usage of fluid powered downhole motors for bit rotation instead of surface drill string rotation and inasmuch as percussion drilling has proven to be effective, the present invention provides a means for adding the benefits of percussion drilling to such pre-existing drill motors.
The apparatus of the present invention provides for an improved method for drilling earthen boreholes with a fluid powered rotary motor mounted on the downhole end of a non-rotating, fluid conducting drill string. The central shaft of a fluid powered, axially reciprocating hammer is coupled to the motor by means of a rotary coupling having freedom for axial movement, so that the hammer will be rotated by the motor and the motor will be axially isolated from the reciprocating hammer. The percussion hammer comprises a reciprocating mass, in the form of an annular piston operating on the central shaft to impact the drilling bit on its down stroke. The motor is powered by fluid conducted from the surface through the drill string according to the well known practice of prior art. In the present invention however, drilling fluid discharged from the motor is utilized at lower pressure for and controlled by valving ports integral to the central shaft so as to power reciprocation of the piston. Upon discharge from the percussion hammer, the drilling fluid circulates through the bit to flush the borehole and carry the cuttings up the annulus around the the drill string to the well surface.
The present invention eliminates the extended drill string length between the surface motor and the percussion tool, so as to eliminate the quick reacting wound-up forces and axial forces which otherwise conspire to inhibit motor isolation. Thus, the percussive blows reach the splined coupling with a sharpness that overcomes static friction in the splines of a connecting coupling coupling and a heretofore unrealized degree of motor isolation is achieved.
Since the output torque and rotational speed of the generic motors varies with the particular design, operational pressure and other factors, the percussion hammer should be sized, tuned and made suitable for the characteristics of each motor as well as the field application. For example a higher speed lower torque output motor would require a relatively light, higher frequency hammer to bit impact while a higher torque lower speed motor could have a higher hammer to bit impact.